A miniaturized multipass cell for measurement of O2 concentration in vials based on TDLAS. (April 2023)

• Record Type: Journal Article
• Authors: Yang, Tianyue; Wu, Xuechun; Guo, Guqing; Guo, Xu; Gong, Ting; Tian, Yali; Sun, Xiaocong; Qiu, Xuanbing; Yang, Huinan; Fittshen, Christa; Li, Chuanliang
• Is Part Of: Optics and lasers in engineering. Volume 163(2023)
• Publication Date: 2023-04
• Subjects: Vial inspection -- Miniaturized multipass cell -- O2 -- TDLAS; Lasers in engineering -- Periodicals; Optical measurements -- Periodicals; Optics -- Periodicals; Lasers en ingénierie -- Périodiques; Mesures optiques -- Périodiques; Optique -- Périodiques; 621.36605
• DOI: 10.1016/j.optlaseng.2022.107454
• Languages: English
• ISSNs: 0143-8166

Abstract

Highlights: A miniaturized multipass cell (MMPC) was developed for enhancing the effective optical path within the vial. The interference of ambient O2 was significantly suppressed due to the compact construction. The beam pattern on the mirrors was calculated according to the analytical vector method. The sensitivity with respect to the vial position was investigated for testing the robustness of the MMPC within a production chain. The O2 concentration in the vial was measured by MMPC in combination with calibration-free. Abstract: Tunable diode laser absorption spectroscopy (TDLAS) is an effective method to inspect possible leakage during filling. However, the sensitivity of TDLAS is confined by the optical path length of the vial headspace. In this letter, the development of a miniaturized multipass cell (MMPC) for improving the sensitivity of laser spectrometer for detecting the O2 content in vial headspaces is presented. Based on analytical vector calculation, a few types of MMPC have been designed and their corresponding beam distributions are derived. The beam spots on the mirrors are compressed in a line-shape parallel with the vial, given the limitation of vial headspace. The simulated configuration with the minimum open path-length is then used for an experimental validating of the MMPC. The horizontal position of the vial has only little influence on the output laser power in the range of -0.5–0.5 mm relative to the optimum one, which is acceptable for practical applications. Wavelength modulation spectroscopy of calibration-free TDLAS was employed to measure the O2 concentration. It is demonstrated that the signal-to-noise ratio improves by 6 times compared to single pass configuration. The R 2 of linear fitting the O2 concentration against signal amplitude could reach 0.998 in the range of 0–21% O2 . According to the Allan variance analysis, the minimum detection sensitivity of the system is estimated at 0.05% at 141 s.